How else can we recharge our batteries, other than from the rooftop solar panel?
Running the vehicle engine will provide electrical current to charge our house batteries, via the vehicle alternator and our Redarc DC-DC charger. The Sprinter alternator can produce up to 60 Amps – but how much current feeds to the batteries depends on the capacity of your battery charger / regulator and how it profiles the charging current.
The Redarc BCDC 1240D regulator/charger fitted to our van has a maximum charge capacity of 40 amps. So, driving the vehicle for one hour will (in theory) replenish a maximum of 40 Ah battery capacity – though this is not likely to be the reality, as battery chargers regulate the current flowing to the batteries as the batteries’ charge level increases. This is particularly the case with AGM batteries.
However, charging the batteries from the alternator for an hour or so will certainly get you out of trouble and keep your fridge cold.
Portable solar panel
A portable solar panel can be used to supplement the electric current generated by the roof-top panel, at similar rates to the roof-top panel (up to 7 amps from a 150W panel, up to 10 amps from a 200W panel).
A portable solar panel can be more efficient than your rooftop panel, because the portable panel can be continually repositioned to ‘follow the sun’ for maximum current generation.
We have fitted an external Anderson Plug to our van’s electrical system, to provide a connection point for an additional solar panel. The cabling from the Anderson Plug has been connected to feed current generated by the external panel directly to the Redarc DC-DC regulator, negating the need for an additional external regulator.
External solar panels are available as solid folding units (aluminum frame with glass covers) or, more recently, as foldable mats (pictured). If purchasing a folding panel or a mat, check the weight and the size of the panel when it is folded for traveling. (We recently purchased a Kings 200W solar mat that folds down to 360mm x 380mm x 75mm, weighing 7kg.)
An external solar panel is also handy when camped under trees – the external panel can be located in sunshine away from the vehicle. 6mm diameter cables are the minimum size for external cable leads, to reduce voltage drop. 8mm connecting cables should be used for cable leads longer than 5 metres. 10 metres is about the maximum practical cable length before current drop (due to cable resistance) becomes a significant issue.
Ideally, an external panel can be connected to your existing regulator/charger – depending on the capacity and specifications of your charger. Alternatively, an external panel can be connected to your batteries via a secondary regulator/controller. This regulator should be located at the ‘battery end’ of the connecting cable, rather than at the ‘panel end’, to minimize charging current loss due to the resistance of the cable.
There are two types of regulators supplied with most portable panels – either PWM or MPPT. If you have a choice, go for an MPPT model. (Read more about regulators / controllers)
How many Amps?
An inline power meter is a great accessory to keep you in the charging loop, displaying how many amps are feeding into your battery/s (via your battery charger).
These meters are widely available from camping / electronics retailers and will give you a real-time readout of Amps, Watts and Volts from your external solar blanket or panel. Anderson plugs make it simple to connect into the line between your panel and charger..
230V AC Mains Power
Our built-in CTEC M25 AC-DC charger will recharge the batteries up to the rate of 25 amps per hour, when an external AC power supply is connected. This current is regulated by the charger in the same way as the DC-DC charger – Boost and Absorption stages (and a Float stage for AGM batteries).
The CTEC AC-DC charger and the Redarc DC-DC charger (feeding charging current from the solar panels and alternator) are independent devices and can both be charging the batteries at the same time.
If you are considering the installation of Lithium batteries, makes sure that your chargers, both DC-DC and AC-DC, have a Lithium charging profile.
Not something we have considered, but a fuel-powered generator can be used to provide a charging connection to the van. This is something of a ‘last resort’, as generators are bulky items to carry (along with fuel) and are not popular with other campers in quiet campsites!
This is all good in theory, but what are your power limits when your are out camping in the real world? The next section – The Bottom Line – discusses the realities of a sustainable 12V power supply.